ASHRAE Research Project 1480 Report - Food Service Technology ...

Perforated Perimeter Supply
Four perforated perimeter supply (PPS) plenums were used as part of the local makeup air
investigation. Each was 1.0 foot deep by 0.5 feet tall. Two of the plenums measured 10.0 feet
wide and two measured 8.0 feet wide. The four PPS’s were balanced with the factory louvers and
additional dampers at the two 28.0-inch by 10.0 inch inlets to each PPS.
The velocity from the face of each PPS was measured with a 4-inch rotating vane anemometer at
three airflow rates. Each reading was an average of two single point measurements located at the
center of 1 square foot areas along the PPS, with the anemometer held at a distance of 2.0 inches
from the face of the PPS. Figure 20 shows an example of the velocity readings in feet per minute
with the PPS supply rate at 160 cfm per foot of PPS, or 5760 cfm.
306 264 215 180 363 340 300 258 227 286
301 202 236 293 261 162 146 192
208 181 166 267 187 175 185 291
PPS MUA
187 248 296 269 372 364 211 219 278 330
Displacement MUA
Figure 20. Velocity Profile for PPS's at 160 cfm/ft or 5760 cfm
To ensure the reported airflow rates were accurate, the measured airflow rates to the PPS’s were
verified. Since the laboratory is airtight, it was known that air into the laboratory must equal air
out of the laboratory. Exhaust fan speeds were established for the three PPS airflow rates while
all other supply air sources were disabled and sealed. The PPS ductwork was then disconnected
and sealed, and the front displacement ventilation system was enabled, with its own independent
airflow measurement stations. The exhaust fan speed was then reestablished and the airflow was
2-19
RP-1480